Most synthetic polymer materials undergo deterioration when exposed to light and elevated temperatures over a prolonged period of time. Some polymers are so sensitive to heat that they will degrade objectionably even during the relatively short period of time they are exposed to elevated temperatures during many types of compounding and processing operations. The degradation effects of heat and light on polymers often can be at least temporarily retarded by mixing a heat and light stabilizer (normally referred to as a "primary stabilizer") with the polymer. The particular primary stabilizer chosen will depend upon the polymer to be stabilized.
Chlorine-containing synthetic polymers (whether the chlorine atom is introduced as a part of a monomer or is added by the post-chlorination of a previously formed polymer) are quite susceptible to heat degradation at most normal processing temperatures and, as a consequence, stabilization of the polymer is of significant importance.
Typical primary stabilizers used commercially for stabilizing chlorine-containing polymers include a wide variety of materials such as the barium, cadmium, zinc, tin and lead salts of monocarboxylic acids and the organotin and organoantimony stabilizers. Generally, from about 0.5 to 5.0 parts by weight of a primary stabilizer is used per 100 parts by weight of the polymer. However, even with the addition of a primary stabilizer, the polymer composition often is not sufficiently heat-stabilized to permit the composition to be used in processing techniques that require the composition to be heated to moderately high temperatures (for example, product forming by injection molding). Also, the cost of many of the preferred primary stabilizers is relatively high. Accordingly, stabilizer systems which provide better heat stabilization at a reduced cost are sought by the industry.